Of all the disasters that regularly strike India, floods are possibly the most recurrent and impact large areas. India is one of the most flood-prone countries of the world, with 23 out of the 35 states and Union Territories vulnerable to floods (Source: MHA). In terms of geographical area, about one-eighth or 40 million hectares of land are prone to flooding, with 8 million hectares prone to annual flooding.

All river basins of India are vulnerable to floods. The main causes of devastating floods are attributed to heavy rainfall and antecedent conditions of catchment area, inadequate drainage, or breach in flood control structures like embankments and levees. Poor permeability of soil causes flash floods as water fails to seep down to deeper layers. Human interventions like constructions on riverbeds, poor planning and implementation, poor storm-water drainage and sewerage are main causes of urban floods.

Tropical Cyclone

According to the World Meteorological Organization (WMO), tropical cyclones are weather systems "in which winds exceed gale force (34 knots or 63 kmph)". A combination of warm sea temperatures, high relative humidity and atmospheric instability results in the formation of a tropical cyclone. These disasters are characterised by destructive winds, storm surges and torrential rain causing massive community disruption.

A long coastline of 7516 Km has resulted in India's exposure to nearly 10% of all tropical cyclones. On an average, 5-6 tropical cyclones occur in a year in India, mostly in the Bay of Bengal. Post-monsoon cyclones occur most frequently and are generally more devastating in intensity. It is estimated that 58% of the cyclonic storms that form in the Bay of Bengal hit the coast in October and November. Strict implementation of Coastal Zone Regulations, efficient early warning dissemination mechanisms and construction of cyclone shelters and cyclone resistant housing practices are important mitigation measures to reduce the risk.

Tsunami

Tsunamis result due to vertical movement of the sea floor due to tectonic causes and result in vertical displacement of the overlying water column. This produces gigantic waves which travel at about 800 kmph and hits the coast as a wall of water destroying everything in its path. Tsunami wavers may be amplified by bathymetric features, making its height vary from coast to coast.
The most recent and devastating tsunami that hit the Indian coast on 26 December 2004 led to a loss of 9395 lives and affecting 26.63 lakh people. The east and west coast of India and the island regions are vulnerable to tsunamis potentially generated by the subduction zone movement in Andaman-Nicobar-Sumatra Island Arc and the Makran area north of Arabian Sea.